The fabrication of semiconductors utilizes wafers of silicon basically comprising thin slices from large cylindrical crystalline ingots. Typically, such ingots must first be machined into the cylindrical shape by grinders, leaving relatively short cone-shaped sections on one end of the cylindrical ingot and a longer, tapered, irregular-shaped tail section. Both the cone and tail sections must first be removed, typically by way of an inner diameter diamond circular saw blade, in order to facilitate further processing of the cylindrical ingot. Because its generally longer taper makes for a greater moment arm, the tail section is readily removable by the saw blade without any problems.
However, as the inner diameter saw blade cuts through the cone-shaped end of the ingot, a vacuum is often produced in the space between the blade and the cone section being removed, due in part to the narrow gap between the planar surface of the saw blade and the cut portion of the wall of the ingot, in part to the greater cross-sectional area being cut, and in part to the extremely-high velocity (ca. 1100 rpm) of the saw blade. The so-created vacuum tends to pull the section of the ingot being cut into the blade, thereby creating a number of problems: friction between the ingot and the saw blade reduces blade life and increases saw downtime; resultant shear stress on the outer portion of the uncut crystal can lead to chips and cracks in the crystal upon completion of the cut, thereby reducing the yield of useable crystalline ingot; and, on occasion, due to the build-up of vacuum between the blade and the section being cut, the entire section being cut will adhere to the spinning blade, the blade then often throwing the cut piece into the mounting assembly of the blade, which in turn results in catastrophic failure of the blade and severe damage to the cut end of the ingot.
The conventional way of dealing with all of the aforesaid problems is to affix a mass of clay or putty to the end of the ingot that is being cut off. However, this method has a number of engineering drawbacks, chief among which is the difficulty of molding the clay or putty into the proper size and shape so that it will not only stick to the end of the ingot being cut off but at the same time provide sufficient moment to eliminate the vacuum yet not so great a moment as to cause the uncut section of the crystalline ingot to break. Another significant drawback with this prior art method comes into play by virtue of the extremely sensitive slicing machine sensors which are very diameter-sensitive; improper placement of the clay or putty can and often does confuse the machine's sensors, resulting in the cut being made at an improper location. Still another draw-back is the safety-related problem comprising imbedment of sharp silicon shards in the putty during cutting which shards tend to cut operator's hands when the putty is removed and/or reattached to a new ingot.
There is therefore a need in the art of making endcuts from silicon ingots for a method or device which will provide an adjustable moment on the section of ingot that is being cut off, the device being securely attachable to that section and being reusable, so as to eliminate the creation of a vacuum and at the same time not generate sufficient downward force to cause premature breakage of the section being cut off from the ingot. These needs and others are met by the present invention, which is summarized and described in detail below.